$ tlmgr install pdfcrop
Useless content call in void context at /usr/share/perl5/LWP/Protocol/ftp.pm line 379.
TLDownload::get_file: response error: 400 FTP return code 000 (for ftp://tug.org/historic/systems/texlive/2015/tlnet-final/tlpkg/texlive.tlpdb.md5)
TLUtils::download_file: persistent connection ok, but download failed: ftp://tug.org/historic/systems/texlive/2015/tlnet-final/tlpkg/texlive.tlpdb.md5
TLUtils::download_file: retrying with wget.
TLUtils::download_file: retry with wget succeeded: ftp://tug.org/historic/systems/texlive/2015/tlnet-final/tlpkg/texlive.tlpdb.md5
No connection to the internet.
Unable to download the checksum of the remote TeX Live database,
but found a local copy so using that.

You may want to try specifying an explicit or different CTAN mirror;
see the information and examples for the -repository option at
http://tug.org/texlive/doc/install-tl.html
(or in the output of install-tl --help).

TeX Live 2015 is frozen forever and will no
longer be updated.  This happens in preparation for a new release.

If you're interested in helping to pretest the new release (when
pretests are available), please read http://tug.org/texlive/pretest.html.
Otherwise, just wait, and the new release will be ready in due time.
tlmgr: package repository ftp://tug.org/historic/systems/texlive/2015/tlnet-final
[1/2, ??:??/??:??] install: pdfcrop.i386-linux [1k]
TLDownload::get_file: response error: 401 Sorry, the maximum number of clients (3) from your host are already connected. (for ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.i386-linux.tar.xz)
TLUtils::download_file: persistent connection ok, but download failed: ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.i386-linux.tar.xz
TLUtils::download_file: retrying with wget.
TLUtils::download_file: retry with wget failed: ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.i386-linux.tar.xz
Downloading
   ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.i386-linux.tar.xz
did not succeed, please retry.
TLPDB::_install_package: couldn't unpack ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.i386-linux.tar.xz to /path/to/texlive/2014
[2/2, 00:30/21:00] install: pdfcrop [15k]
TLDownload::get_file: response error: 401 Sorry, the maximum number of clients (3) from your host are already connected. (for ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.tar.xz)
TLUtils::download_file: persistent connection ok, but download failed: ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.tar.xz
TLUtils::download_file: retrying with wget.
TLUtils::download_file: retry with wget failed: ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.tar.xz
Downloading
   ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.tar.xz
did not succeed, please retry.
TLPDB::_install_package: couldn't unpack ftp://tug.org/historic/systems/texlive/2015/tlnet-final/archive/pdfcrop.tar.xz to /path/to/texlive/2014
tlmgr: package log updated: /path/to/texlive/2014/texmf-var/web2c/tlmgr.log